An outboard engine includes an internal combustion engine and a cowling covering the engine and other components of the power head so as to prevent them from being damaged by water, salt, wind and other such exterior elements.
A flywheel is typically mounted to an end of the crankshaft of the outboard engine to help maintain a constant angular velocity between engine firings. The flywheel also helps to start the engine. For both rope-pull engines and those with electric starters, the momentum of the flywheel smoothes out the force required to overcome compression within the cylinders in order to force the crankshaft to turn and thereby commence operation of the engine.
The outboard engine also includes a generator for generating electrical energy for operation of various electrically powered sub-systems. The generator is typically an alternator comprising a rotor and a stator, and more specifically a magneto comprising a plurality of permanent magnets. The rotor is typically attached to the flywheel. The stator, which includes a plurality of coils, is bolted to the engine block. The rotation of the rotor induces a current in the stator coils, which is used to charge the batteries and to power the various sub-systems.
The fresh air drawn into the cowling typically flows through the engine compartment, from a cowling inlet to a throttle body, before entering the combustion the engine's chambers. The rapidly rotating flywheel mounted atop the engine generates a significant amount of air turbulence within the engine compartment, which results in a more chaotic air flow from cowling inlet to throttle body, which in turn results in increased heat transfer from the engine to the air. In addition, the stator coils generate a considerable amount of heat which further increases the temperature of the air in the engine compartment. Heat transfer to the air within the engine compartment can have a negative impact on engine performance as the hotter the air drawn into the engine for the combustion process, the lower the efficiency and power output of the engine. It is thus desirable to minimize this heating of air in the engine compartment before entering the engine.